. Chronic rejection and long-term graft loss are significant problems in human organ transplantation. The applicants have shown, in preliminary experiments with rats, that allograft survival can be improved by the administration of donor bone marrow cells that have been co-cultured with splenocytes. The cultured cells can be fractionated, with some fractions having more activity than others, thereby allowing better phenotype definition of the active cell type(s). The applicants propose to culture human bone marrow, examining different culture conditions in order to obtain an analogous cell population with human cells. The cells will be characterized and compared to the rat culture results, with the ultimate goal being the use of cultured, and perhaps fractionated, human bone marrow cells in human organ transplantation to induce tolerance. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE